In the prior art, silicon oxide powder is produced, as disclosed in JP-A 63-103815, by heat treating a raw material mixture containing silicon dioxide base oxide powder in a reduced pressure, non-oxidizing atmosphere to generate SiO vapor, and condensing the SiO vapor in a gas phase, thereby continuously forming fine amorphous SiO particles with a size of 0.1 μm or less. Alternatively, silicon raw material is heated, evaporated and deposited on a surface of a substrate having a coarse structure as disclosed in JP-A 9-110412.
The method of JP-A 63-103815 is capable of continuous production, but fails to produce high purity silicon oxide powder because the SiO powder produced is a fine powder which undergoes oxidization when taken out in the air. The method of JP-A 9-110412 can produce high purity silicon oxide powder, but does not lend itself to mass-scale production since it is of batchwise design. As a consequence, the silicon oxide powder becomes expensive.